Electromagnetic time element device



Jan. '11, 1944. F. H. WINTER 2,339,125

ELECTROMAGNETIC TIME ELEMENT DEVICE Filed July 21, 1942 Inventor": Fr-ed H.Wir1ter',

by W 6'. His Att or'ney.

Patented Jan. 11, 1944 ELECTROMAGNETIC TIME ELEMENT DEVICE Fred H. Winter, Schenectady, N. Y,, assignor to General Electric Company. a corporation of New York Application July 21, 1942, Serial No. 451,737

3 Claims.

My invention relates to electromagnetic time element devices, particularly to time delay switches or contactors such as used in the starting of electric motors, and has for its object simple and reliable means for compensating the con tactor for the change in its magnetic forc and time characteristic caused by changes in the temperature of its magnetic circuit.

My invention is especially applicable to electric relays or contactors provided with an operating coil and a restraining or lockout coil for restraining when energized the armature against the force applied by the operating coil. In such devices the operating coil is energized continuously during the operation of the motor and, consequently, its temperature, including the temperature 01 its magnetic iron, rises very c nsiderably. On the other hand, the lockout. coil is energized only momentarily during the starting of the motor and. consequently, does not have an opportunity to heat to any considerable extent. Thus, the pick-up force of the operating coil gradually decreases with use over an extended period of time, whereas the magnetic force of the lockout coil does not change appreciably. As a result of the decrease in the force of the operating coil, the time interval required for the operating coil to pick up its armature increases with consequent decrease in the rate of acceleration of the motor.

In carrying out my invention in one form, I provide a layer of thermomagnetic metal in the magnetic circuit'of the lockout coil but adjacent the operating coil so as to be heated by the operating coil. Thus, as the temperature of the operating coil increases, the temperature of the thermomagnetic or Curie metal increases with consequent decrease in the force of the lockout coil. As a result. the timeof operation of the switch remains substantially unchanged.

' For a more complete understanding of my invention, reference should be had to the accompanying drawing, Fig. 1 of which is a view in section of a time delay contact such as used in the starting of electric motors embodying my invention while Fig. 2 is a simplified diagram of an electric motor starting system utilizing the contactor of Fig. 1.

Referring to the drawing, I have shown my invention in one form .as applied to a time delay starting contactor of a system of the type described and claimed in Patent 2,233,169, issued on February 25, 1941 to Benjamin W. Jones.

This contactor is provided with an operating coil in and with a lockout coil ii. The armature i2 is pivotaily mounted on a knife edged bearing support It and suitably biased by gravity tc the unattracted position shown in Fig. 1. A magnetic core 14 extending through the coil ill attracts the lower end of the armature when the coil ill is energized, the magnetic circuit for the coil in beingcompleted by a core member IS.

The upper portion or extension iii on the armature overlaps the end of a core member ll extending across the outer end of the lookout coil Ii. A central core member I8 extends through the coil Ii and has its ends engaging the core member i5 and the core member 17.

In accordance with my invention, I provide a layer 19 made of a thermomagnetic material or Curie metal whose magnetic permeability decreases with an increase in temperature, such as an alloy of nickel and iron containing 32 per cent nickel and 68 per cent iron. This layer i9 is placed between the end of the core member i8 and the core member I5 so as to be in engagement with the core member i5 and therefore be heated by conduction therefrom in accordance with the temperature rise in the operating coil iii.

Referring to Fig. 2 of the drawing, in the starting of an electric motor 20 provided with a start-- ing resistance 2|, the operating coil i0 is connected across the supply mains, and also the lookout coil ii is connected across the supply mains in series with an interlock switch 22. To provide a time delay, a suitable electric ener y storage device, such as a capacitor 23, is connected in parallel with the lookout cell it.

In operation, when the motor is at rest or starting, the switch 22 is closed and the two coils are energized, the lockout coil ii holding the armature I? in its unattracted position and therefore holding open the short-circuiting switch 26 operated by the armature i2. During the starting of the motor, the switch 22 is opened as by the closing of the preceding contactor or by a manually operated controller whereby the lockout coil ii is disconnected from the supply source. The capacitor 23 then discharges through the lookout coil and maintains the energization of the lockout coil sufficiently high over a predetermined interval of time to prevent pick-up of the armature i2 and therefore prevent closure of the short-circuiting switch M for that appreciable interval of time. interval, the coil Ii has become so weakened that it is overpowered by the coil l0 and the armature picked up to close the switch 28.

Thereafter, during the running operation of the motor, the coil to remains energized and At the end of the time consequently its temperature rises. The coil heats the core member I whose permeability is thereby decreased with consequent decrease in the operating force of the coil applied to the armature. The lockout coil ll, however, is not energized at this time and therefore its temperature does not rise except for the heat that is conducted to it from the coil i0. However, the layer IQ of thermomagnetic material is heated directly by the coil I and is responsive to the temperature of the coil I 0. Thus its magnetic permeability decreases. Its thickness and change in permeability with increased temperature are such as to introduce a magnetic flux resistance in the magnetic circuit of the lockout coil of such value as to decrease the permeability of this magnetic circuit in substantial proportion to the decrease in permeability of the magnetic circuit oi the coil "I. As a result, when the motor 20 is stopped after running for a time sufficient to heat the coil ID to a high temperature and then immediately restarted, the time control in the closing of the switch 24 remains substantially unchanged.

0n the other hand, without the layer of thermal magnetic material IS; the time interval of the contactor is very considerably inncreased, sometimes as much as 25 per cent, with consequent proportionate increase in the starting time of the motor 20.

It will be observed that the magnetic flux path for the coil II with the coil in energized is through the central core i8, the magnetic frame members I! and i8. the armature i2 and the central core l4 back to the core it. Also, some of the flux of the coils returns through the core member I5. The two coils ordinarily are energized in such directions that their fluxes are in th same direction through the core members I4 and I8. A substantial portion of the magnetic flux produced by the coil i0 passes through the, flux path in parallel with the core member l5 of my invention, it will be understood, of course,

that I do not wish to be limited thereto since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination in an electromagnetic time element device of an operating coil, a magnetic core for said coil arranged to reduce the operating force of said coll when said core is heated by energization of said operating coil, a lookout coil arranged when energized to oppose said operating coil, and a separate magnetic core member for said lockout coil including a member made of thermomagnetic material heated by said op erating coil thereby to maintain a predetermined relation between the forces of said coils and a predetermined time interval in the operation of said operating coil after said lockout coil is disconnected from its supply source.

2. The combination in an electromagnetic time element device of an operating coil, an armature for said coil movable from an unattracted to an attracted position upon energization of said operating call, a lookout coil for holding said armature in said unattracted position for a predetermined time interval after said lockout coil is disconnected from its electric supply source against the force applied by said operating coil when said operating coil is energized, a magnetic core for said lockout coil including a member made of thermomagnetic material in heat conductive relation with said operating coil for decreasing the permeability of said core in response to the temperature of said operating coil so as to maintain said tim interval substantially constant.

3. The combination in an electric time element device of a pair of core members arranged in end-to-end axial alignment with respect to each other, an operating coil mounted on a first of said cores, a lookout coil mounted on the secend of said cores, an armature member pivotally mounted to be moved by said first core to an at tracted position upon energization of said operating coll, a first switch operated by said armature member and movable to a closed position by movement of said armature member to its attracted position, a magnetic member secured to the outer end of said second core extending to a position to be engaged by said armature when said armature is in its unattracted position so that said lockout coil when energized restrains said armature against movement by said operating coil to said attracted position, a second switch connected in circuit with said lockout coil and movable to its open position to deenergize said lockout coil thereby to provide for movement of said armature to said attracted Position and closure of said first switch by said operating coil, said operating coil heating said first core so as to materially decrease the permeability of said first core and decrease the magnetic attraction of said core on said armature, and a layer of thermomagnetic material interposed between said core members so as to be heated from said first core member thereby to decrease the permeability of ,said second core member in substantial proportion to the decrease in permeability of said first core member and maintain substantially unchanged the time interval of operation of said armature to its attracted position after said lockout coil is deenergized.

FRED H. WINTER. 

